The primary feature of class A buildings is the fireproofed structural steel frame, which may be welded, bolted or riveted together. The fireproofing may be masonry, poured concrete, plaster, sprayed fiber or any other method, which gives a high fire-resistance rating.
Floor and roof in class A structures are normally reinforced concrete on steel decking or formed slabs resting on the frame or poured to become integral with it. They may also be composed of prefabricated panels and may be mechanically stressed.
Exterior walls are curtain walls of masonry, concrete, steel studs and stucco, or one of the many types of panels of metal, glass, masonry or concrete. Interior partitions frequently are of masonry or gypsum block, although many movable and lightweight steel partitions are used.
Included in this class are Uniform, Basic and Standard Building Code construction, Types I and II (noncombustible) and ISO classes 5 and 6, if the framing is protected steel. ISO class 5 and 6 buildings with load-bearing walls and no interior framing, and most low-rise buildings, should be classified as class C for pricing purposes. This class is also referred to as Modified Fire Resistive or Two to Four-hour construction.
Class B: Reinforced Concrete Frame
The primary characteristic of class B buildings is the reinforced concrete frame in which the columns and beams can be either formed or precast concrete. They may be mechanically stressed. Class B buildings are fire-resistant structures.
Floors and roofs in class B structures are formed or precast concrete slabs. The exterior walls, generally, are masonry or reinforced concrete curtain walls or any of the many types of wall panels of concrete, metal, glass or stone. In some class B buildings the walls may be partially load bearing. Interior partitions are often masonry, reinforced concrete or gypsum block. Many lightweight and movable partitions are used where structural walls are not needed.
Included in this class are Uniform, Basic and Standard Building Code construction, Types I and II (noncombustible) and ISO classes 5 and 6, if the framing is concrete. ISO class 5 and 6 buildings with load-bearing walls and no interior framing and most low-rise buildings should be classified as class C for pricing purposes. This class is also referred to as Fire Resistive or Two to Four-hour construction.
Class C: Masonry Bearing Walls
Masonry or reinforced concrete (including tilt-up) construction characterizes class C buildings. The walls may be load-bearing, i.e., supporting roof and upper floor loads, or nonbearing with concrete, steel or wood columns, bents or arches supporting the load. Wood or steel joists or trusses support upper floors and roofs. Ground floors may be concrete slabs. Upper floors may be of concrete plank, steel deck or wood. Bearing walls are frequently strengthened by concrete bond beams and pilasters. Class C buildings are not fire-resistant structures.
Included in this class are Uniform and Basic Building Code, Type III (noncombustible wall), Standard Code Type V and ISO classes 2 and 4, and those ISO class 5 and 6 buildings that have load-bearing walls without interior framing and of low-rise design (3 stories or less). This class is also referred to as Masonry or Unprotected
Noncombustible, Joisted or Unprotected Masonry, or Ordinary or Unprotected One- hour, and includes certain Two-hour or heavy timber construction.
Class D: Wood- or Steel-Framed Exterior Walls
Class D buildings are characterized by combustible construction. The exterior walls may be made up of closely spaced wood or steel studs, as in the case of a typical frame house. Exterior covers may be wood siding, shingles, stucco, brick or stone veneer or some other type of material.
Floors and roofs are supported on wood or steel joists or trusses. The floor may be a concrete slab on the ground.
Construction Type V (wood-frame) of the Uniform, Type IV Basic and Type VI Standard Building Code are included in this class, as are ISO class 1 buildings. This class is also referred to as Unprotected-protected One-hour Construction.
Class H: Hoop Frame
Class H (a subset of Class D) buildings are characterized by combustible prefabricated wood post and tubular steel semicircular (hoop – quonset shape) framed roofs that curve to a short wooden pony wall or to the ground. The roof and walls are generally covered with canvas or a woven vinyl tarp. Ground floors are typically dirt or can be a concrete slab.
Construction Type V (wood-frame) of the Uniform, Type IV Basic and Type VI Standard Building Code are included in this class, as are ISO Class 1 buildings. This class is also referred to as Unprotected-protected One-hour Construction.
Class M: Mill Type Construction
Class M buildings are characterized by heavy masonry and timber construction. The walls are generally thick load-bearing brick or non-bearing with open wood columns, trusses or arches supporting the load. Floors are heavy laminated wood or a concrete slab on the ground.
Included in this class are Uniform and Basic Building Code, Type III (noncombustible wall), Standard Code Type V and ISO classes 2 and 4, and those ISO class 5 and 6 buildings that have load-bearing walls without interior framing and of low-rise design (3 stories or less). This class is also referred to as Masonry or Unprotected
Noncombustible, Joisted or Unprotected Masonry, or Ordinary or Unprotected One- hour, and includes certain Two-hour or heavy timber construction.
Class P: Wood Frame and Metal Walls (Pole Frame)
Class P buildings (a subset of Class D) are characterized by combustible prefabricated wood structural members. The exterior walls are comprised of an open-wood-
skeleton post frame and trusses, with exterior coverings of prefabricated metal panels or sheet siding. Wall girts span between posts and there can be an in-fill of wood studs. Upper floors are supported on wood joists or trusses. The roof is supported by prefabricated trussed-rafters with wood purlins or nailers. Ground floors are typically concrete slabs or can be dirt.
Construction Type V (wood-frame) of the Uniform, Type IV Basic and Type VI Standard Building Code are included in this class, as are ISO Class 1 buildings. This class is also referred to as Unprotected-protected One-hour Construction.
Class S: Metal Frame and Walls
Class S buildings are characterized by incombustible construction and prefabricated structural members. They are not fire-resistant buildings. The exterior walls may be steel studs or an open-steel-skeleton frame with exterior coverings of prefabricated panels or sheet siding. Upper floors and roof are supported on steel joists or beams. Ground floors are typically concrete slabs.
Included in this class are Uniform and Standard Building Code construction, Type IV (noncombustible), Basic code Type V and ISO class 3 buildings. This class is also referred to as Noncombustible and can be One-hour Type II construction.
Class W: Metal Slant Frame and Walls
Class W buildings (a subset of Class S) are characterized by incombustible
construction and light prefabricated structural members. They are not fire-resistant buildings. The exterior walls and roof coverings are prefabricated metal panels or sheet siding supported by an open-steel-skeleton slant (modified A) frame. Ground floors are typically concrete slabs.
Included in this class are Uniform and Standard Building Code construction, Type IV (noncombustible), Basic Code Type V and ISO Class 3 buildings. This class is also referred to as Noncombustible.